C programming notes
Contents
^ Overview
This page to hold notes and links to C programming resources and reference materials. A language standards document is available at https://www.open-std.org/jtc1/sc22/WG14/www/docs/n1256.pdf.
A good tool to aid writing C code is the indexing utility known as `ctags`:
^ C Qualifiers and Type Casting
^ Serial Port Use in C
- https://tldp.org/HOWTO/Serial-Programming-HOWTO/
- https://tldp.org/HOWTO/Serial-Programming-HOWTO/x115.html
// Example 3.2 code from https://tldp.org/HOWTO/Serial-Programming-HOWTO/x115.html
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
#include <stdlib.h> //echo "z" >> /dev/ttyS1 to provide exit()
// https://man7.org/linux/man-pages/man3/bzero.3.html
#include <strings.h> // to provide bzero()
// https://man7.org/linux/man-pages/man2/read.2.html
// https://linux.die.net/man/3/read
#include <unistd.h> // to provide read()
#define BAUDRATE B38400
//#define MODEMDEVICE "/dev/ttyS1"
#define MODEMDEVICE "/dev/ttyUSB0"
#define _POSIX_SOURCE 1 /* POSIX compliant source */
#define FALSE 0
#define TRUE 1
volatile int STOP=FALSE;
int main(void)
{
int fd, c, res;
struct termios oldtio,newtio;
char buf[255];
printf("Starting,\nopening serial device '%s' . . .\n", MODEMDEVICE);
fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY );
if (fd <0) {perror(MODEMDEVICE); exit(-1); }
tcgetattr(fd,&oldtio); /* save current port settings */
bzero(&newtio, sizeof(newtio));
// newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
newtio.c_cflag = BAUDRATE | CS8 | CLOCAL | CREAD;
newtio.c_iflag = IGNPAR;
newtio.c_oflag = 0;
/* set input mode (non-canonical, no echo,...) */
newtio.c_lflag = 0;
newtio.c_cc[VTIME] = 0; /* inter-character timer unused */
newtio.c_cc[VMIN] = 5; /* blocking read until 5 chars received */
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);
printf("looping to read from serial port . . .\n");
while (STOP==FALSE) { /* loop for input */
res = read(fd,buf,255); /* returns after 5 chars have been input */
buf[res]=0; /* so we can printf... */
printf(":%s:%d\n", buf, res);
if (buf[0]=='z') STOP=TRUE;
}
tcsetattr(fd,TCSANOW,&oldtio);
return 0;
}
^ Co-routines
Interesting article by Simon Tatham on co-routines and a couple ways of implementing them in C language; accessible good style of writing:
Quote from the article:
- <! -- not intended use for ul tag -->
"Any coding standard which insists on syntactic clarity at the expense of algorithmic clarity should be rewritten." - Simon Tatham
Floating point convert and notes on-line, Javascript converter:
^ C Pointers and dereference syntax
This section the beginning of references, links and personal notes on some of the most difficult and important C language constructs, often used in schedulers and RTOS implementations:
Arrays of strings and arrays of pointers to strings:
^ Simple C examples
Program 1 - use of C comma operator, a binary operator:
#include <stdio.h>
#include <stdlib.h>
// Compile with:
//
// $ gcc -Wall main.c
//
// As of 2022-06-09 Builds with 'gcc (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0'
int main(int argc, char *argv[])
{
int z = 3;
int y[(z++, (z + 1))];
y[0] = 1;
if ( z == y[0] ) { }
#define SIZE_OF_160_BYTES (160)
char lbuf[SIZE_OF_160_BYTES] = { 0 };
snprintf(lbuf, SIZE_OF_160_BYTES, "2022-06-09 main.c test of C comma operator\narray y[] has size of %lu\n",
sizeof(y));
printf("%s", lbuf);
return 0;
}
^ C Macros
This section likely to grow as C macros have a development history somewhat separate from the development of C language itself, and extensive use being both powerful and prone to pitfalls.
Articles on the use of C language 'do while(0)' construct in macros. The do while(0) construct is the only C syntax which expands correctly from C macros regardless of the use of curly braces and semicolons around the given macro.
A useful macro pair, and this must be a macro pair, is the following set of defines. These defines will accept a string and put double quotes around it:
#define MAKE_STRING_QUOTED(string) #string #define WRAPPER_NEEDED_TO_QUOTE_STRING(token) MAKE_STRING_QUOTED(string)
One Guy Rutenberg explains this C pre-processor pattern:
This C macro pattern is explained a number of other places as well.
The `__fallthrough()` macro appears to be a C++ macro. It may be found among Zephyr RTOS 3.4.0 source tree contents. An article on the concept of "fall through" in C switch statements:
^ References
